Why cant I use a reference to class object within its constructor when passing to another object

game.cpp

#include "game.h"Game::Game() : tileMap(mapRows, mapCols),               player(this),{...}

When instantiating the Game class, I pass a pointer reference of this class to player.

When instantiating player I want to use a function within tileMap

However I cannot access game pointer due to it being an incomplete type.

Why can't I access it?

IGameActor.h

class Game; // Forward declaration of Game classclass IGameActor {protected:    Game* game; // Pointer to the Game objectpublic:    virtual ~IGameActor() {}      IGameActor(Game* gamePtr) : game(gamePtr) {}    IGameActor() : game(nullptr) {}

player.h

class Player : public IGameActor {  public:    Player(Game* game);    virtual void update(float dt) = 0;}

player.cpp

Player::Player(Game* game) : IGameActor(game) { ... }void Player::update() {    std::cout << game->name;}

./build.shsrc/entities/player.cpp: In member function ‘virtual void Player::update(float)’:src/entities/player.cpp:54:22: error: invalid use of incomplete type ‘class Game’   54 |     std::cout << game->name;      |                      ^~In file included from include/entities/player.h:5,                 from src/entities/player.cpp:1:include/entities/IGameActor.h:7:7: note: forward declaration of ‘class Game’    7 | class Game; // Forward declaration of Game class      |       ^~~~Compilation failed.